Mould damage in a rented room: defect or use?

This article describes the situation in the Netherlands and is not legal advice. Put agreements in the housing agreement and the house rules, and ask a lawyer for advice in a dispute.

01Two kinds of cause

Under Dutch tenancy law, mould is a defect (gebrek) that the landlord is responsible for when it arises through no fault of the tenant: through rising damp, a thermal bridge, or ventilation or heating that falls short even with proper use. The tenant, in turn, has to heat and ventilate properly, and the landlord does well to explain how.

In the buildingDefect

Thermal bridge or poor insulation
Leak or rising damp
Ventilation not working

The wall stays cold or wet, even with proper heating and airing.

From how people liveUse

Drying laundry in the room
Vents closed, window never open
Room kept too cold

Humidity peaks that linger, on an otherwise healthy wall.

Who pays depends on the cause. Readings per room show which of the two it was.

Cause	Examples	Usually rests with
The building	Thermal bridge, leak, rising damp, defective ventilation or heating	Landlord
The use	Not ventilating, vents closed, laundry drying in the room, heating always off	Resident

In practice both often play a part. A wall that is just too cold only grows mould if too much moisture also stays in the room. That is exactly why it helps to know what happened in the room.

Cross-section of an outside wall. On the inside of the cold wall, humidity rises above 80 %, and that is where mould starts.

02What readings show

A sensor that measures temperature and humidity every ten minutes shows a pattern for each room. Each cause has its own pattern.

Too little ventilation

Humidity rises after showering, cooking or at night, and then hardly falls. The room stays above 65 to 70 % for days while the temperature is normal. That usually points to the use, unless the ventilation is defective: vents closed, laundry in the room, windows that never open.

A cold wall

Humidity in the room is normal, around 50 to 60 %, but the mould is in one spot: a corner, a window frame, behind a wardrobe against the external wall. Then that spot is too cold. Adding the outdoor temperature, it can be estimated that the humidity at that surface went above 80 %, even with reasonable use. That points to the building. A wardrobe pushed right up against the external wall makes it worse; that belongs in the house rules too.

A cold room

The room stays below 16 to 17 °C for days. That can be a fault, such as a closed valve or a defective radiator, or a resident who switches the heating off. The readings show when it started; the house's fault reports show whether something was broken.

A leak

Humidity rises without a fixed pattern and stays high, even when nobody is home or when the room is being ventilated. Then there may be water in the structure.

03A record per room

What keeps a dispute afterwards short:

photos and a short description at move-in and at move-out;
the explanation about ventilation, recorded in writing in a language the resident can read;
readings from day one, so you can see how the room behaved before and during the stay;
the alerts, and what was done next: a conversation, a dryer, a repair.

04Preventing is cheaper than proving

The best record is one you never need. If a room is red for two weeks, a talk with the resident or a dryer in the hallway costs less than repainting plus a dispute over the deposit that nobody wins. eyesonrooms estimates the mould risk on the coldest wall for every room and reports it, with address and room, long before anything is visible. Read more about the causes in Preventing mould in worker housing.

A record per room, from day one

Readings are kept as agreed with you and can be exported. A pilot shows within a month which rooms are at risk.

Request a pilot

Or look at the pricing first: €47.99 per sensor, €89.99 per gateway and €4.99 per room per month (incl. VAT), both with a volume discount from 40 rooms.

05Frequently asked questions

Can I deduct mould damage from the deposit?

Only if the damage was caused by the use of the room, you can back that up, and your agreements allow it. If in doubt, get legal advice.

Do readings help once the mould is already there?

Yes. After cleaning and repair, the readings show whether the room still gets too damp. That tells you quickly whether the cause has really gone.

How long are the readings kept?

For as long as agreed with the customer in the data processing agreement. When a resident moves out, you can export the room's history and add it to the file.

Mould damage in a rented room: building defect or use?